AEP-7862: Make API changes for CPU Startup boost

[kamarabbas99]

What type of PR is this?

/kind documentation
/kind feature

What this PR does / why we need it:

Which issue(s) this PR fixes:

These changes are based on discussion in
#8175 (comment) https://kubernetes.slack.com/archives/C0EG7JC6T/p1751910562504969

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[APPROVALNOTIFIER] This PR is NOT APPROVED

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[kamarabbas99]

/unassign laoj2 omerap12

[kamarabbas99]

/cc laoj2 omerap12

[adrianmoisey]

/ok-to-test

[adrianmoisey]

cc @raywainman @soltysh

[omerap12]

Thanks for opening this and updating the AEP.
We should also include the expected Go struct definition. From what I understand, it should look like this:

// +enum
type CPUBoostType string

const (
    FactorType   CPUBoostType = "Factor"
    QuantityType CPUBoostType = "Quantity"
)

type CPUStartupBoost struct {
    // +unionDiscriminator
    // +required
    Type CPUBoostType `json:"type"`

    // +unionMember=Factor
    // +optional
    FactorValue *int32 `json:"factorValue,omitempty"`

    // +unionMember=Quantity
    // +optional
    Quantity *resource.Quantity `json:"quantity,omitempty"`

    // +optional
    Duration *metav1.Duration `json:"duration,omitempty"`
}

[raywainman]

/lgtm

I'll let @adrianmoisey or @omerap12 approve since they were heavily involved in the discussion.

[adrianmoisey]

What happens if the recommendation is higher than the boosted value, during the boost period?

[kamarabbas99]

During the boost period, the VPA updater ignores new recommendations, and the pod continues to run with its boosted CPU value.

[adrianmoisey]

Yup, makes sense. Is it worth calling that out in the AEP?
I think there are 3 things worth calling out explicitly:

1. the feature will base the boosted value on the recommendation at time of admission
2. no resizing will take place during boost
3. during unboost, the pod will be resized to whatever the recommendation is at that moment in time

At least, those bullet points are how I understand the AEP to work

[laoj2]

+1, it's also important to callout that the feature will ignore the recommendation if the VPA updateMode=Off (or containerScalingMode=Off)

[laoj2]

I just realized we do mention the updateMode already :), is it worth it mentioning containerScalingMode too?

[laoj2]

nit: can you also mention the updates in the history log?

[omerap12]

overall /lgtm. please address @adrianmoisey and @laoj2 comments :)